light-year

noun

ˈlīt-ˌyir 

1

: a unit of length in astronomy equal to the distance that light travels in one year in a vacuum or about 5.88 trillion miles (9.46 trillion kilometers)

2

: an extremely large measure of comparison (as of distance, time, or quality)

seems like light-years ago

has light-years more talent

two minutes and yet light-years away from the crowded village

—Suzanne Patterson

Synonyms

• galaxy
• world

Examples of light-year in a Sentence

my sister and I are close in age, but personality-wise, there are light-years between us

Recent Examples on the Web

Located 15,000 light-years from Earth, at the end of an outer spiral arm of our Milky Way galaxy, Sh2-284 lacks elements heavier than hydrogen and helium, much like the environment of the early universe, according to a statement from NASA. —Samantha Mathewson, Space.com, 21 Mar. 2025

Barnard’s Star is small—about 15 percent the mass of our sun—and only around six light-years away. —Rudy Molinek, Smithsonian Magazine, 20 Mar. 2025

In a surprise siting around 590 million light-years from Earth, light from a background galaxy curved around a foreground galaxy (NGC 6505) and created a brilliant ring. —Jack Knudson, Discover Magazine, 19 Mar. 2025

Astronomers have confirmed the existence of four planets orbiting a star less than 6 light-years away with help from some of the world's most powerful telescopes. —Julia Jacobo, ABC News, 18 Mar. 2025

Word History

First Known Use

1864, in the meaning defined at sense 1

Rhymes for light-year

• atmosphere
• biosphere
• centromere
• chemosphere
• chromosphere
• hemisphere
• hydrosphere
• lithosphere
• mesosphere
• microsphere
• miserere
• mountaineer

Kids Definition

light-year

noun

ˈlīt-ˌyi(ə)r

1

: a unit of length in astronomy equal to the distance that light travels in one year or 5,880,000,000,000 miles (9,460,000,000,000 kilometers)

2

: a very great distance especially in progress

light-years ahead in design